Presently a number of hydrocarbon drilling techniques have been proposed to better manage pressures within or exerted upon a wellbore during drilling activities. Broadly, these techniques encompass two categories of wellbore pressure control. In the first, a “closed loop” circulating system is employed. This is usually accomplished by installing a rotating control device (“RCD”) similar to that described in, Williams et al U.S. Pat. No. 5,662,181. The RCD is positioned on top of a conventional blow-out preventer. In this system, the RCD directs the flow of drilling mud from inside and atop the wellbore so that drilling mud may be monitored and so the pumping rate can be regulated. In the second, various methods of using multiple columns of drilling fluids with different densities to manipulate the drilling fluid pressure gradient within the wellbore or adding a pumping system to boost wellbore fluids from the well. Fluid density levels effect the fluid pressure gradient within the wellbore and help boost fluids from the well.
Due to limitations in the physical characteristics of existing marine risers present pressure management techniques cannot be implemented without substantial additional cost and/or time. For example, the method and apparatus disclosed in U.S. Pat. No. 6,273,193 (Hermann et al) employs a concentric inner riser and related elements (support, sealing mechanisms, etc.). However, the Hermann et al method and apparatus require the marine riser system to be substantially disassembled before the concentric riser can be deployed. Disassembling the marine riser system adds significant time and cost to the drilling operation. Additionally, the system of Hermann et al leaves the upper end of the marine riser system unpinned to the underside of the rig. This results in the potential for differential movement of the riser away from the well centerline that could cause eccentric side loading of wellbore annular sealing element. Further, the Hermann et al method employs the upper annular blow-out preventer of the existing BOP to effectively seal and isolate the annulus between the lower end of the concentric riser and the lower end of the marine riser rendering it unavailable for its primary well control function.
Hannegan et al. U.S. Pat. No. 6,263,982 describe a method and apparatus where a RCD is installed on top of a marine riser in a manner similar to Hermann et al method and apparatus. The Hannegan method and apparatus has similar limitations with respect to the time and cost of installing and operating the system. Additionally, without an concentric riser, the burst pressure capacity of the conventional marine riser limits the maximum annular pressure that may be imposed.
The present invention overcomes these limitations by enabling a conventional marine riser that is easily configured and reconfigured to conduct dual gradient and annular drilling capabilities.